One form of electrostatographic copying involves the use of a photosensitive member comprised of a conductive substrate having on its surface a layer of photoconductive material which is, in turn, overcoated with a layer of an insulating resin. This sort of photosensitive member is useful in the xerographic induction imaging process described by Butterfield in U.S. Pat. No. 2,693,416; Hall in U.S. Pat. No. 3,234,019; Mitsui in IEE Transactions on Electron Devices, April 1972 (Pp. 396-404); Nakamura in IEE Transactions on Electron Devices, April 1972 (Pp. 405-412) and Mark in Photographic Science and Engineering, May/June 1974 (Pp. 254-261).
In addition, a novel gravure imaging system is disclosed in U.S. Pat. No. 3,801,315. This system employs a gravure member having a conductive backing with a uniform pattern of lands and valleys thereon, the lands having a surface of a photoconductive insulating material. A liquid developing medium is applied to the valleys of the gravure member, leaving the land areas substantially clean. After application of the developing liquid, the gravure member is uniformly charged and then exposed to a light and shadow image. Exposure of the charged surface discharges those areas which are irradiated and leaves the unexposed portions of the lands in the charged state to form a latent electrostatic image. The liquid developing material in the valleys is electrostatically attracted to the charged areas and will be caused to flow up to the charged areas of the lands by this electrostatic attraction to develop the latent image on the lands of the gravure member.
The gravure member, in a preferred embodiment, is a cylindrical surface with the lands and valleys on the surface in helicoid configuration. Such a member can be made by uniformly coating the cylindrical surface, which must be electrically conducting, with a layer of a photoconductive insulating material and then milling the cylinder to form valleys in the desired configuration. The milling operation will tend to remove the photoconductor from the milled areas thereby providing a gravure member with lands having a film of photoconductive material separated by valleys in which the conductive substrate is exposed. In the alternate embodiment, specifically disclosed in Example 6 of U.S. Pat. No. 3,801,315, the photoconductive material completely covers the surface of the gravure member. In this embodiment, in which it is necessary to use a developing medium which is opaque to the radiation used to image the member, a reversed or negative image is obtained. A gravure member useful in this embodiment could be prepared by applying a thin layer of photoconductive material to the cylindrical substrate after it has been milled to form the lands and valleys in helicoid configuration. In either case, fabrication of the gravure member presents problems because of the fine tolerances required during the milling operation.
It would be desirable and it is an object of the present invention to provide a novel electrostatographic photosensitive device which is useful in the above-described imaging methods.
It is an additional object to provide a novel photosensitive device comprising a substrate, which need not necessarily be conductive, and a layer of photoconductive material over said substrate which is, in turn, overcoated with a dielectric storage layer.
Another object is to provide a novel method for fabricating such a device.
A further object is to provide a novel gravure member for the previously described liquid developed copying method.
An additional object is to provide such a gravure member which can be readily fabricated to fine tolerances.
A further object is to provide such a gravure member in which the substrate need not necessarily be electrically conductive.
Another object is to provide a novel method for the preparation of such a gravure member.